feat(python): add license support for requirement.txt files

docs/docs/coverage/language/python.md

@@ -3,20 +3,20 @@
 Trivy supports three types of Python package managers: `pip`, `Pipenv` and `Poetry`.
 The following scanners are supported for package managers.
 
-| Package manager | SBOM  | Vulnerability | License |
-| --------------- | :---: | :-----------: | :-----: |
-| pip             |   ✓   |       ✓       |    -    |
-| Pipenv          |   ✓   |       ✓       |    -    |
-| Poetry          |   ✓   |       ✓       |    -    |
+| Package manager | SBOM | Vulnerability | License |
+|-----------------|:----:|:-------------:|:-------:|
+| pip             |  ✓   |       ✓       |    ✓    |
+| Pipenv          |  ✓   |       ✓       |    -    |
+| Poetry          |  ✓   |       ✓       |    -    |
 
 In addition, Trivy supports three formats of Python packages: `egg`, `wheel` and `conda`.
 The following scanners are supported for Python packages.
 
-| Packaging | SBOM  | Vulnerability | License |
-| --------- | :---: | :-----------: | :-----: |
-| Egg       |   ✓   |       ✓       |    ✓    |
-| Wheel     |   ✓   |       ✓       |    ✓    |
-| Conda     |   ✓   |       -       |    -    |
+| Packaging | SBOM | Vulnerability | License |
+|-----------|:----:|:-------------:|:-------:|
+| Egg       |  ✓   |       ✓       |    ✓    |
+| Wheel     |  ✓   |       ✓       |    ✓    |
+| Conda     |  ✓   |       -       |    -    |
 
 
 The following table provides an outline of the features Trivy offers.
@@ -40,6 +40,8 @@ See [here](./index.md) for the detail.
 Trivy parses your files generated by package managers in filesystem/repository scanning.
 
 ### pip
+
+#### Dependency detection
 Trivy only parses [version specifiers](https://packaging.python.org/en/latest/specifications/version-specifiers/#id4) with `==` comparison operator and without `.*`.
 To convert unsupported version specifiers - use the `pip  freeze` command.
 
@@ -91,7 +93,16 @@ urllib3==1.26.15
 `requirements.txt` files don't contain information about dependencies used for development.
 Trivy could detect vulnerabilities on the development packages, which not affect your production environment.
 
-License detection is not supported for `pip`.
+#### License detection
+
+`requirements.txt` files don't contain information about licenses.
+Therefore, Trivy checks `METADATA` files from `lib/site-packages` directory. 
+
+Trivy uses 3 ways to detect `site-packages` directory:
+
+- Checks `VIRTUAL_ENV` environment variable.
+- Detects path to `python`[^1] binary and checks `../lib/pythonX.Y/site-packages` directory.
+- Detects path to `python`[^1] binary and checks `../../lib/site-packages` directory.
 
 ### Pipenv
 Trivy parses `Pipfile.lock`.
@@ -116,4 +127,6 @@ Trivy looks for `*.egg-info`, `*.egg-info/PKG-INFO`, `*.egg` and `EGG-INFO/PKG-I
 ### Wheel
 Trivy looks for `.dist-info/META-DATA` to identify Python packages.
 
+[^1]: Trivy checks `python`, `python3`, `python2` and `python.exe` file names.
+
 [dependency-graph]: ../../configuration/reporting.md#show-origins-of-vulnerable-dependencies

pkg/fanal/analyzer/language/python/pip/pip.go

@@ -2,31 +2,92 @@ package pip
 
 import (
 	"context"
+	"fmt"
+	"io"
+	"io/fs"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"sort"
+	"strings"
 
+	"github.com/samber/lo"
 	"golang.org/x/xerrors"
 
+	goversion "github.com/aquasecurity/go-version/pkg/version"
+	"github.com/aquasecurity/trivy/pkg/dependency/parser/python/packaging"
 	"github.com/aquasecurity/trivy/pkg/dependency/parser/python/pip"
 	"github.com/aquasecurity/trivy/pkg/fanal/analyzer"
 	"github.com/aquasecurity/trivy/pkg/fanal/analyzer/language"
 	"github.com/aquasecurity/trivy/pkg/fanal/types"
+	"github.com/aquasecurity/trivy/pkg/log"
+	"github.com/aquasecurity/trivy/pkg/utils/fsutils"
 )
 
 func init() {
-	analyzer.RegisterAnalyzer(&pipLibraryAnalyzer{})
+	analyzer.RegisterPostAnalyzer(analyzer.TypePip, newPipLibraryAnalyzer)
 }
 
 const version = 1
 
-type pipLibraryAnalyzer struct{}
+var pythonExecNames = []string{
+	"python3",
+	"python",
+	"python2",
+	"python.exe",
+}
+
+type pipLibraryAnalyzer struct {
+	logger         *log.Logger
+	metadataParser packaging.Parser
+}
+
+func newPipLibraryAnalyzer(_ analyzer.AnalyzerOptions) (analyzer.PostAnalyzer, error) {
+	return pipLibraryAnalyzer{
+		logger:         log.WithPrefix("pip"),
+		metadataParser: *packaging.NewParser(),
+	}, nil
+}
+
+func (a pipLibraryAnalyzer) PostAnalyze(_ context.Context, input analyzer.PostAnalysisInput) (*analyzer.AnalysisResult, error) {
+	var apps []types.Application
 
-func (a pipLibraryAnalyzer) Analyze(_ context.Context, input analyzer.AnalysisInput) (*analyzer.AnalysisResult, error) {
-	res, err := language.Analyze(types.Pip, input.FilePath, input.Content, pip.NewParser())
+	sitePackagesDir, err := a.pythonSitePackagesDir()
 	if err != nil {
-		return nil, xerrors.Errorf("unable to parse requirements.txt: %w", err)
+		a.logger.Warn("Unable to find python `site-packages` directory. License detection is skipped.", log.Err(err))
+	}
+
+	// We only saved the `requirements.txt` files
+	required := func(_ string, _ fs.DirEntry) bool {
+		return true
+	}
+
+	if err = fsutils.WalkDir(input.FS, ".", required, func(pathPath string, d fs.DirEntry, r io.Reader) error {
+		app, err := language.Parse(types.Pip, pathPath, r, pip.NewParser())
+		if err != nil {
+			return xerrors.Errorf("unable to parse requirements.txt: %w", err)
+		}
+
+		if app == nil {
+			return nil
+		}
+
+		// Fill licenses
+		if sitePackagesDir != "" {
+			for i := range app.Packages {
+				app.Packages[i].Licenses = a.pkgLicense(app.Packages[i].Name, app.Packages[i].Version, sitePackagesDir)
+			}
+		}
+
+		apps = append(apps, *app)
+		return nil
+	}); err != nil {
+		return nil, xerrors.Errorf("pip walt error: %w", err)
 	}
-	return res, nil
+
+	return &analyzer.AnalysisResult{
+		Applications: apps,
+	}, nil
 }
 
 func (a pipLibraryAnalyzer) Required(filePath string, _ os.FileInfo) bool {
@@ -41,3 +102,128 @@ func (a pipLibraryAnalyzer) Type() analyzer.Type {
 func (a pipLibraryAnalyzer) Version() int {
 	return version
 }
+
+// pkgLicense parses `METADATA` pkg file to look for licenses
+func (a pipLibraryAnalyzer) pkgLicense(pkgName, pkgVer, spDir string) []string {
+	// METADATA path is `**/site-packages/<pkg_name>-<pkg_version>.dist-info/METADATA`
+	pkgDir := fmt.Sprintf("%s-%s.dist-info", pkgName, pkgVer)
+	metadataPath := filepath.Join(spDir, pkgDir, "METADATA")
+	metadataFile, err := os.Open(metadataPath)
+	if os.IsNotExist(err) {
+		a.logger.Debug("No package metadata found", log.String("site-packages", pkgDir),
+			log.String("name", pkgName), log.String("version", pkgVer))
+		return nil
+	}
+
+	metadataPkg, _, err := a.metadataParser.Parse(metadataFile)
+	if err != nil {
+		a.logger.Warn("Unable to parse METADATA file", log.String("path", metadataPath), log.Err(err))
+		return nil
+	}
+
+	// METADATA file contains info about only 1 package
+	// cf. https://github.com/aquasecurity/trivy/blob/e66dbb935764908f0b2b9a55cbfe6c107f101a31/pkg/dependency/parser/python/packaging/parse.go#L86-L92
+	return metadataPkg[0].Licenses
+}
+
+// pythonSitePackagesDir returns path to site-packages dir
+func (a pipLibraryAnalyzer) pythonSitePackagesDir() (string, error) {
+	// check VIRTUAL_ENV first
+	if venv := os.Getenv("VIRTUAL_ENV"); venv != "" {
+		libDir := filepath.Join(venv, "lib")
+		if _, err := os.Stat(libDir); os.IsNotExist(err) {
+			return "", xerrors.Errorf("unable to detect `lib` dir for %q venv: %w", venv, err)
+		}
+
+		spDir, err := a.findSitePackagesDir(libDir)
+		if err != nil {
+			return "", xerrors.Errorf("unable to detect `site-packages` dir for %q venv: %w", spDir, err)
+		} else if spDir != "" {
+			return spDir, nil
+		}
+	}
+
+	// Find path to Python executable
+	pythonExecPath, err := pythonExecutablePath()
+	if err != nil {
+		return "", err
+	}
+	pythonExecDir := filepath.Dir(pythonExecPath)
+
+	// Search for a directory starting with "python" in the lib directory
+	libDir := filepath.Join(pythonExecDir, "..", "lib")
+	spDir, err := a.findSitePackagesDir(libDir)
+	if err != nil {
+		return "", xerrors.Errorf("unable to detect `site-packages` dir for %q: %w", pythonExecPath, err)
+	} else if spDir != "" {
+		return spDir, nil
+	}
+
+	// Try another common pattern if the Python library directory is not found
+	spDir = filepath.Join(pythonExecDir, "..", "..", "lib", "site-packages")
+	if fsutils.DirExists(spDir) {
+		return spDir, nil
+	}
+
+	return "", xerrors.Errorf("site-packages directory not found")
+}
+
+// pythonExecutablePath returns path to Python executable
+func pythonExecutablePath() (string, error) {
+	for _, execName := range pythonExecNames {
+		// Get the absolute path of the python command
+		pythonPath, err := exec.LookPath(execName)
+		if err != nil {
+			continue
+		}
+		return pythonPath, nil
+	}
+	return "", xerrors.Errorf("unable to find path to Python executable")
+}
+
+// findSitePackagesDir finds `site-packages` dir in `lib` dir
+func (a pipLibraryAnalyzer) findSitePackagesDir(libDir string) (string, error) {
+	entries, err := os.ReadDir(libDir)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return "", xerrors.Errorf("failed to read lib directory: %w", err)
+		}
+		return "", nil
+	}
+
+	// Find python dir which contains `site-packages` dir
+	// First check for newer versions
+	pythonDirs := a.sortPythonDirs(entries)
+	for i := len(pythonDirs) - 1; i >= 0; i-- {
+		dir := filepath.Join(libDir, pythonDirs[i], "site-packages")
+		if fsutils.DirExists(dir) {
+			return dir, nil
+		}
+	}
+	return "", nil
+}
+
+// sortPythonDirs finds dirs starting with `python` and sorts them
+// e.g. python2.7 => python3.9 => python3.11
+func (a pipLibraryAnalyzer) sortPythonDirs(entries []os.DirEntry) []string {
+	var pythonVers []goversion.Version
+	for _, entry := range entries {
+		// Found a directory starting with "python", assume it's the Python library directory
+		if entry.IsDir() && strings.HasPrefix(entry.Name(), "python") {
+			ver := strings.TrimPrefix(entry.Name(), "python")
+			v, err := goversion.Parse(ver)
+			if err != nil {
+				a.logger.Debug("Unable to parse version from Python dir name", log.String("dir", entry.Name()), log.Err(err))
+				continue
+			}
+			pythonVers = append(pythonVers, v)
+		}
+	}
+
+	// Sort Python version
+	sort.Sort(goversion.Collection(pythonVers))
+
+	return lo.Map(pythonVers, func(v goversion.Version, _ int) string {
+		return "python" + v.String()
+	})
+}